The invention relates to a speed control system and method having a distance sensor, which is intended for a motor vehicle (the motor vehicle having the distance sensor being the “ego vehicle”).
Speed control systems having an automatic distance control, also called ACC (“Active Cruise Control” or “Adaptive Cruise Control”), have been known in the automobile trade, including in the applicant's vehicles, for several years. They basically permit two modes: traveling on a clear stretch of road at a predetermined desired vehicle speed when no vehicle (object) driving ahead is detected, and following another vehicle at a predefined desired distance, when a vehicle driving ahead is detected as a target object. From a technical point of view, such speed control systems can be understood to be an expansion of the conventional cruise control by use of a distance sensor, which supplies information, such as distance and speed of additional vehicles (objects) in the driving environment of the ego vehicle to the ACC controller. At first, these ACC systems were conceived only for use on turnpikes (autobahn) and well developed highways and expressways and were limited to a speed range above 30 km/h. Especially, the operation of such systems in a traffic jam was therefore not possible. This gap, however, was closed by the next generation of such systems, the so-called ACC stop-and-go systems.
An ACC stop-and-go system decelerates the ego vehicle to a stationary position and automatically causes it to start moving again within certain time thresholds in order to follow a vehicle traveling in front. The form of this ACC stop-and-go system, however, has the disadvantage of not reacting to a-priori stationary vehicles, thus to vehicles that had never been detected by the sensor as driving, as, for example, the end of a line of vehicles at a red traffic light. The reason is the central technical problem of the ACC systems. It is not sufficient to detect objects from the traffic environment; rather, it also has to be decided whether these objects are in their own traffic lane. This objective is achieved only insufficiently so that there may be a considerable number of erroneous reactions to vehicles in neighboring traffic lanes. Since, as a rule, the distance sensors detect a much higher number of stationary objects (guard rails, traffic signs, bridges, etc.) than moving objects, a general addition of the stationary objects to the potential target objects would result in an unacceptable increase in erroneous brakings.
A speed control system which partially also already includes stationary objects in the control, is known from European Patent document EP 1 304 251 B1. However, in this case, only a braking to the stationary position is taken into account.
It is an object of the invention to further develop a speed control system of the above-mentioned type with a view to preventing erroneous braking while including (a-priori) stationary objects.
This and other objects are achieved according to the invention by a speed control system having a distance sensor for a motor vehicle (ego vehicle), which, in a first mode in the form of traveling on a clear stretch of road, sets a predefined desired vehicle speed and, in a second mode in the form of following another vehicle, sets a predefined minimum distance to a selected target object. The target object in the second mode is selected according to a first selection process which screens out stationary objects as target objects. When at least one defined condition is present, a transition takes place starting from the first mode into a third mode in the form of a decelerated travel, during which a second selection process is started which evaluates also stationary target objects, and during which, until a target object is selected, the vehicle is traveling on a clear road stretch with the initiation of a deceleration with respect to following another vehicle. When a target object is selected by the second selection process, a switch-over immediately takes place from the third mode into the second mode.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.